Pretty much what the title says. Can't rise the rpm any higher than that from the BIOS. And I'm pretty sure the stock fan should reach at least 5000 rpm.
Some more info:
Motherboard-->Asrock N68-GS4 FX.
PSU-->EVGA 600B 80 plus.
Maximum fan speed can vary by OEM boxed fan provided. The fan speed will also change based on CPU temp/load unless you manually override it to run at a certain speed. You should however be able to adjust the fan speed to 100% or maximum in the BIOS and/or the Operating System. You may be required in some O/S's such as Win 10 to use a maximum performance "Power Plan" for both maximum fan speeds as well as proper use of ALL CPU cores.